ATMEGA32(2008) Просмотр технического описания (PDF) - Atmel Corporation

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ATMEGA32
(Rev.:2008)

8-bit Microcontroller with 32K Bytes In-System Programmable Flash

Atmel Corporation 

ATmega32(L)

Table 7. External RC Oscillator Operating Modes

CKSEL3..0

Frequency Range (MHz)

0101

0110

0.1 - 0.9

0.9 - 3.0

0111

3.0 - 8.0

1000

8.0 - 12.0

When this Oscillator is selected, start-up times are determined by the SUT fuses as shown in

Table 8.

Table 8. Start-up Times for the External RC Oscillator Clock Selection

SUT1..0

00

Start-up Time from

Power-down and

Power-save

18 CK

Additional Delay

from Reset

(VCC = 5.0V)

–

Recommended Usage

BOD enabled

01

18 CK

4.1 ms

Fast rising power

10

18 CK

65 ms

Slowly rising power

11

6 CK(1)

4.1 ms

Fast rising power or BOD enabled

Note: 1. This option should not be used when operating close to the maximum frequency of the device.

Calibrated Internal

RC Oscillator

The Calibrated Internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All fre-

quencies are nominal values at 5V and 25°C. This clock may be selected as the system clock by

programming the CKSEL fuses as shown in Table 9. If selected, it will operate with no external

components. The CKOPT Fuse should always be unprogrammed when using this clock option.

During Reset, hardware loads the calibration byte for the 1MHz into the OSCCAL Register and

thereby automatically calibrates the RC Oscillator. At 5V, 25°C and 1.0 MHz Oscillator fre-

quency selected, this calibration gives a frequency within ± 3% of the nominal frequency. Using

calibration methods as described in application notes available at www.atmel.com/avr it is possi-

ble to achieve ± 1% accuracy at any given VCC and Temperature. When this Oscillator is used

as the Chip Clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the

reset time-out. For more information on the pre-programmed calibration value, see the section

“Calibration Byte” on page 258.

Table 9. Internal Calibrated RC Oscillator Operating Modes

CKSEL3..0

0001(1)

Nominal Frequency (MHz)

1.0

0010

2.0

0011

4.0

0100

8.0

Note: 1. The device is shipped with this option selected.

29

2503N–AVR–06/08

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